For the past 20 years, this grant has been instrumental in supporting and developing the activities of the Rheumatic Diseases Study Group. The main activities for which support is requested are the following: 1) Amino acid sequence studies of the products of naturally occurring mutation of immunoglobulin producing cells in man in the hope of gaining insight into the organization of the immunoglobulin genes and to provide information regarding disorders of immunoglobulin synthesis in a variety of neoplastic and non-neoplastic diseases; 2) Studies on the organization of membrane proteins from normal, stimulated and transformed lymphoid cells. Amino acid sequence studies of IgD, the major immunoglobulin of lymphoid membranes are also contemplated; 3) Studies of the factors regulating immunoglobulin synthesis and assembly in a variety of disease states and under normal conditions: (4) Studies of the nature of factors liberated by plasma cell tumors which inhibit the immune response. 2. The role of thymic hormones in the differentiation of lymphoid and other blood forming cells in health and disease.